The present invention is directed to a method of beneficiating material, such as coal, by the sink-and-float process utilizing a dense-media cyclone. More particularly this invention relates to such method in which the separating gravity of the dense-media cyclone is controlled to insure the optimum beneficiation of the treated material.
The use of dense-media separators for segregating material according to its specific gravity is well known in the material separating art, such as the processing of coal. In these separators, a dense-media formed of a finely divided high gravity solid, such as magnetite, suspended in water, is maintained within a vessel, i.e. cyclone. The material or coal to be separated is introduced into the dense-media, and the material or coal which has a specific gravity less than the specific gravity of the suspension reports to the cyclone overflow. For convenience, the coal may be termed the overflow. Material or refuse which has a specific gravity greater than the suspension reports to the cyclone underflow. Thus, the sink material may be termed the underflow.
By the very nature of this beneficiating process, the coal and refuse, overflow and underflow respectively, entrain a certain quantity of the magnetite which must be removed from the coal if the coal is to be thoroughly cleaned for commercial use. Further, recovery of the magnetite, which may be re-used in the process, is necessary for an efficient and economical process. While the present invention relates solely to the primary separation of the coal from the refuse, the magnetite recovery step suggests a further feature of the process, and that is the need to replenish the dense-media suspension. In replenishing the suspension care must be taken to insure a suitable specific gravity within predetermined limits in the cyclone to achieve the primary separation.
A conventional method of controlling the specific gravity of the separating vessel has been for the operator to check the specific gravity of samples of the dense-media at regular intervals and manually make adjustments based on such checks. Another method involves measuring the specific gravity of the media continuously as it enters the vessel and adding water or magnetitie when necessary. Such methods, even when automated, had disadvantages.
U.S. Pat. Nos. 3,246,750 and 3,247,961 (Chase et al), each entitled, "Method and Apparatus for Controlling Specific Gravity in a Heavy Medium Process," teach a system for separating mineral particles, such as coal, which system in part includes "measuring a specific gravity representative of the suspension in the vessel." Based on this measuring, adjustments are made to bring the vessel's specific gravity within predetermined limits.
Controls for the systems described in the above patents rely upon the need to maintain a constancy within the cyclone to obtain an optimum classification of products therefrom.
The present invention represents a unique approach to obtaining a precise separating gravity in a dense-media cyclone using magnetite-water as the slurry therein. Specifically, this invention resulted from the recognition in the processing of coal that there is a correlation between the quantity of magnetite in the cyclone overflow and the separating gravity of the cyclone. The manner by which such recognition has been incorporated into the system of this invention will be described in the following specifications.